Simple model for laser-produced, mass-limited water-droplet plasmas

Plasmas, produced by a neodymium yttrium aluminum garnet (Nd:YAG) laser pulse focused on a small water droplet and used for the generation of extreme ultraviolet light, can be described by a relatively simple model due to the fact that thermodynamic equilibrium can be assumed for the most important phase. Only three time-dependent variables—radius, expansion speed, and internal energy—are needed to describe the physics of the plasma. Nevertheless, it predicts quantities such as the size and the spectrum rather well. It is expected that the theory and the model presented here can also be applied to other laser-produced plasmas.